Plate XVI. 



Palaeostoma mirabile Grät. 



P. 27, 45. 53. 



Fig. 184. A lialf-gTowD specimen, dorsal view. 



Fijf. 185. The same, ventral view. 



Fig. 186. The same, sida view. 



Fig. 187. The peristomal region, with the pentaugular stoma, the valves, the lirst spherids etc. 



Fig. 188. The peristome, with the valves, from the iuside. 



Fig. 189. The valves, from the outside. 



Fig. 190. The calyx with the two sexual pores. 



Fig. 191. The e.Kcretory openiDg with its valves. 



Fig. 192. A phyllodean pedicel. 



Fig. 193. Aiiother phyllodean pedicel, both showing what seems to be a central protuberance. 



Fig. 194. The disk of a frontal pedicel, p. 53. 



Fig. 195. Spicules from a pedicellar tube. 



Fig. 196. A tubercle. 



